To ambulate successfully with an axillary crutch, the upper extremities play an important part in supporting the body's entire weight. To evaluate the roles of the upper extremity during axillary crutch gait 15 normal adult subjects, 23 patients with an affected single leg, and 3 patients with rheumatoid arthritis (RA), were investigated. The gait patterns using crutches were: the one-leg swing-through crutch gait and three-point crutch gait for both normal subjects and patients with an affected single leg, and the three-point crutch gait for RA patients. The real-time motion analysis system "Quick-MAG", force plates, and a VTR system were used for data acquisition. The forces at the arm-pit and the hands during the swing-through crutch gait decreased when the cadence increased from 60 to 100 steps per minute. However, the floor reaction curve suggested distortion of the rubber at the crutch tip when the cadence reached 100. In the plane of progression during the crutch stance phase, the elbow flexion angle was about 14 degrees, and the wrist radial flexion angle about 23 degrees in the middle of the crutch stance phase. This position might be the best for efficient force exertion from the upper extremity. The unloading ratio during the three-point crutch gait was 35 percent in the normal subjects, 49 percent in patients with an affected single leg, and 14 percent in the RA patients. The results of the unloading ratio, indicated that elbow and wrist joint impairment prevented the RA patients from sustaining enough posture to support body weight during the three-point crutch gait.